Nanocrater catalyst in metal nanoparticles and method for preparing the same

ABSTRACT

Disclosed are a nanocrater catalyst in metal nanoparticles with a nanocrater form of hole structure in center of the catalyst which is useful for manufacturing nano-sized materials and/or articles with desired structure and characteristics, a preparation method thereof including a plasma etching and chemical etching process (“PTCE process”), and nano-sized materials and/or articles manufactured by using the nanocrater catalyst in metal nanoparticles.

This application is a Divisional Application of U.S. patent applicationSer. No. 12/000,375, filed on Dec. 12, 2007, which claims priority under35 U.S.C. §119 to Korean Patent Application No. 10-2007-0102100, filedon Oct. 10, 2007, the entire contents of each of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to nanocrater catalyst in metalnanoparticles and their preparation methods, more particularly, to ananocrater catalyst in metal nanoparticles with a nanocrater form ofhole structure at the center of the catalyst, a preparation methodthereof including a plasma etching and chemical etching process (“PTCEprocess”) and nano-sized materials and/or articles manufactured by usingthe nanocrater catalyst in metal nanoparticles.

2. Description of the Related Art

Nano-sized metal particles have electric, optic and/or magneticproperties different from those of bulk metal materials and haverecently received increased attention in a wide range of applications.

Metal nanoparticles having nano-sized holes are possibly combined withadvanced sciences and technologies to be used in a variety ofapplications. Extensive research and investigation into metalnanoparticles is proceeding all over the world, since the metalnanoparticles are absolutely required as a catalyst in production ofnano-sized materials and/or articles.

Accordingly, metal nanoparticles used in production of nano-sizedmaterials closely correlate with structure and characteristics of theresulting nano-sized materials and/or articles. In order to produce adesired product with desired structure and characteristics, there is arequirement to study structure and characteristics of a catalyst, thatis, metal nanoparticles used as the catalyst.

However, there are still serious problems or difficulties in preparationof metal nanoparticles with desired structure and characteristics and,in the present circumstances, studies and developments of the metalnanoparticles have not considerably progressed.

Commonly known methods or technologies in the related arts, for example,electron beam lithography, micro-contact printing, shadow mask and thelike have been employed to control alignment or orientation of particlesand/or particle size. However, such methods have drawbacks in that theseare not commercially available due to high production costs, andsubstrates to be processed are restricted to very small dimensions.

Another method was proposed to provide metal catalysts with uniformdimension using AAO (anodic aluminum oxide) templates. But, commerciallyavailable AAO templates usually have a hole size of more than 100 nm andare substantially unable to have a hole size of less than 50 nmregardless of variation of the processing conditions.

Consequently, there is still a strong demand to develop novel metalcatalysts with controlled structure sufficient to produce nano-sizedmaterials and/or articles having desired structure and characteristics.

SUMMARY OF THE INVENTION

After extensive research and investigation to develop a variety ofnano-sized materials (hereinafter, often referred to as “nanomaterials”) such as carbon nanotubes, the present inventors have foundthat structure and characteristics of nano materials are closelyconnected with structure and characteristics of specific materials usedas a catalyst and, additionally, structure of the catalyst must becontrolled to produce the nano materials with desired structure andcharacteristics. As a result, the present invention was successfullyaccomplished under these findings.

Accordingly, the present invention is directed to solve problems ofconventional methods as described above and, an object of the presentinvention is to provide a nanocrater catalyst in metal nanoparticleswith a nanocrater form of hole structure at the center of the catalyst(hereinafter, often referred to as “nanocrater metal catalyst”) usefulfor manufacturing nano-sized materials with desired structure andcharacteristics.

Another objective of the present invention is to provided a method forpreparing a nanocrater metal catalyst, which can treat massive metalnanoparticles by a simple and economical process.

A still further objective of the present invention is to providenano-sized materials with desired structure (and characteristics)manufactured by using the nanocrater metal catalyst produced accordingto the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objectives, features, aspects, and advantages of thepresent invention will be more fully described in the following detaileddescription of preferred embodiments and examples, taken in conjunctionwith the accompanying drawings. In the drawings:

FIGS. 1A and 1B are scanning electronic microscope (SEM) photographsshowing a nanocrater iron catalyst produced by a general plasma etchingand chemical etching process (PTCE), in particular: FIG. 1A is a SEMphotograph showing a nanocrater iron catalyst formed on a siliconsubstrate; and FIG. 1B is an AFM (atomic force microscope) photographshowing enlarged condition of one particle of the nanocrater ironcatalyst;

FIG. 2A is an AFM photograph showing the nanocrater iron catalyst;

FIG. 2B is a graph illustrating an analysis result of surface height ofthe nanocrater iron catalyst;

FIG. 2C is an AFM photograph showing a nanocrater cobalt catalyst;

FIG. 2D is a graph illustrating an analysis result of surface height ofthe nanocrater cobalt catalyst;

FIGS. 3A to 3E illustrate carbon nitride nanotubes and carbonnanospheres with hollow center structure, both of which are manufacturedusing the nanocrater iron catalyst of the present invention, inparticular: FIG. 3A is a SEM photograph showing carbon nitride nanotubesand carbon nanospheres with hollow center structure; FIG. 3B is a TEM(transmission electronic microscope) photograph showing carbon nitridenanotubes; FIG. 3C is a TEM photograph showing carbon nanosphere withhollow center structure; FIG. 3D is a TEM photograph showing two pairsof carbon nitride nanotubes; and FIG. 3E is a TEM photograph showingenlarged bottom portions of two pairs of carbon nitride nanotubes.

DETAILED DESCRIPTION OF THE INVENTION

In order to achieve the objectives described above, the presentinvention provides a nanocrater catalyst in metal nanoparticles with ananocrater form of hole structure at the center of the catalyst, whichhas vacancy and dislocation between metal nanoparticles of the catalyst,that is, a nanocrater metal catalyst.

The present invention also provides a method for preparing a nanocratercatalyst in metal nanoparticles, comprising the steps of: (a)pre-treating metal nanoparticles vapor-deposited on a substrate withplasma to form vacancy and dislocation between the metal nanoparticles;and (b) chemically etching the metal nanoparticles after the plasmapre-treatment, to form a hole at the center of each of the metalnanoparticles.

Still further, the present invention provides nano-sized materialsmanufactured using the nanocrater catalyst in metal nanoparticles.

The nanocrater metal catalyst of the present invention has advantages inthat: the catalyst is useful for manufacturing a variety of nanomaterials; and has variable sizes and structures to uniformly controlnumber of walls of the nano materials, therefore, can appropriatelycontrol structures of the nano materials such as carbon nanotubes.

An aspect of the present invention provides a nanocrater metal catalystwith a nanocrater form of hole structure at the center of the catalyst,which has vacancy and dislocation between metal nanoparticles of thecatalyst.

The term “nanocrater catalyst” used in the present invention means ametal nanoparticle catalyst with a nanocrater form of hole structure atthe center of each nanoparticle of the catalyst.

Metal ingredient of the nanocrater metal catalyst according to thepresent invention includes, for example, at least one selected fromelements belonging to Groups 3 to 14 in the Periodic Table and,illustrative examples of the metal ingredient are not particularlylimited, but, include Al, Ga, In, Tl, Sn, Pb, Cu, Ag, Au, Zn, Cd, Sc, Y,Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Co, Ni, Ru, Rh, Pd,Os, Ir, Pt and so on. Preferably, the metal ingredient comprises Fe andCo which can be used as a catalyst to grow carbon nanotubes.

As characteristics and structure of nano materials are closely relatedto characteristics and structure of catalyst materials, it is requiredto control structure of the catalyst in order to produce the nanomaterial having desired characteristics and structure. Moreparticularly, since the nanocrater metal catalyst of the presentinvention has a nanocrater form of hole structure, number of walls ofthe nano materials such as carbon nanotubes can be regulated whencontrolling the structure of the catalyst, thereby appropriatelycontrolling thickness of the nano materials, that is, carbon nanotubes.

The nanocrater metal catalyst of the present invention has a nanocraterform of hole structure, which has a size ranging from 1 to 50 nm,preferably, 10 to 20 nm and, more preferably, 14 to 18 nm. If the sizeof the hole is more than 50 nm, the hole is so large over an overallsize of the catalyst that the nanocrater catalyst may not keep itsinherent structure and, thus, cause a problem of not regulating diameterof the nanotubes grown from the nanocrater catalyst in the small range.

The nanocrater metal catalyst of the present invention has thicknessranging from 1 to 20 nm, preferably, 3 to 16 nm and, more preferably, 4to 14 nm. If the thickness is more than 20 nm, the nanocrater catalystalso causes a problem of not regulating diameter of the nanotubes grownfrom the nanocrater catalyst in the small range.

The second aspect of the present invention provides a method forpreparing a nanocrater metal catalyst, comprising the steps of: (a)pre-treating metal thin films vapor-deposited on a substrate with plasmato form vacancy and dislocation between metal nanoparticles of thecatalyst; and (b) chemically etching the metal nanoparticles after theplasma pre-treatment, to form a hole at the center of each of the metalnanoparticles.

In order to prepare the nanocrater metal catalyst of the presentinvention, a metal nanoparticle film vapor-deposited on the substrateundergoes a nitrogen plasma etching process and a subsequent chemicaletching process using an iodine-containing nitric acid/ethanol solution,which is known as PTCE (plasma-treated chemical etching) process.

The plasma pre-treatment in the step (a) is to form vacancy anddislocation between the metal nanoparticles. The substrate is notparticularly limited, but, includes an inorganic substrate fabricated ofsilicon, glass, etc. and an organic substrate fabricated of any oneselected from a group consisting of: polyethylene naphthalate (PEN);polyethylene terephthalate (PET); polycarbonate; polyvinylalcohol;polyacrylate; polyimide; polynorbornene; polyethersulfone (PES) and thelike.

The plasma treatment is preferably conducted under nitrogen gasatmosphere and, the nitrogen gas has a flow rate ranging from 80 to 120sccm (standard cubic centimeters per minute), preferably, 90 to 110sccm, and more preferably, about 100 sccm.

The plasma treatment is preferably conducted with a plasma power rangingfrom 500 to 800 W, and preferably, 600 to 700 W at a temperature rangingfrom 600 to 1,000° C., preferably, 700 to 900° C., and more preferably,900° C.

The present inventive method for preparing the nanocrater metal catalystincludes an additional chemical etching process after the plasmapre-treatment, in order to form a hole at the center of each of themetal nanoparticles. This etching process preferably uses a solution ofethanol/nitric acid containing iodine.

The iodine-containing nitric acid/ethanol solution is a solution mixtureof ethanol and 10 to 30% (v/v) nitric acid containing 1 to 10% by weightof iodine(I) relative to volume of ethanol, which forms vacancy anddislocation between metal nanoparticles generated during the plasmatreatment to produce the hole at the center of each of thenanoparticles.

In the method for preparing the metal catalyst according to the presentinvention, the chemical etching process is conducted for anappropriately controlled term of generally 2 to 4 hours, and preferably,for 3 hours. In case that the chemical etching treatment time exceedsthe above desired range, the etching treatment proceeds in an excess tocause a problem of not maintaining the inherent structure of the metalnanoparticles.

Metal ingredient used in the metal catalyst according to the presentinvention includes, for example, at least one selected from elementsbelonging to Groups 3 to 14 in the Periodic Table and, illustrativeexamples of the metal ingredient are not particularly limited, but,include Al, Ga, In, Tl, Sn, Pb, Cu, Ag, Au, Zn, Cd, Sc, Y, Ti, Zr, Hf,V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt,etc. Preferably, the metal ingredient comprises Fe and Co which can beused as a growth catalyst of carbon nanotubes.

The third aspect of the present invention provides nano materialsmanufactured using the nanocrater metal catalyst of the presentinvention.

Illustrative examples of such nano materials are not particularlylimited, but, include nanotube, nanorod, nanowire, nanoneedle,nanoparticle and the like.

For carbon nanotubes according to an embodiment of the presentinvention, these are fabricated by using the nanocrater metal catalystwith a nanocrater form of hole structure, and thus, have a constantnumber of walls. As a result, the fabricated nanotubes have specificcharacteristics and structure such as uniform diameter size.

Hereinafter, the present invention will become apparent from thefollowing examples and experimental examples with reference to theaccompanying drawings. However, these are intended to illustrate theinvention as preferred embodiments of the present invention and do notlimit the scope of the present invention.

Example 1 Preparation of Nanocrater Iron Catalyst

For preparation of a nanocrater iron catalyst, first of all, an ironfilm with a thickness of about 10 nm was vapor-deposited on a siliconsubstrate at 200° C. by means of a sputtering process. Then, thedeposited substrate was plasma etched using 100 sccm of nitrogen gaswith a plasma power of 600 W at 800° C. for 1 minute.

Among the above processes, the metal films separated and etched in therange of nano units by the plasma treatment process produced a pluralityof vacancies and dislocations in inherent structure of the metalnanoparticles. Next, after preparing an iodine-containing nitricacid/ethanol solution which was a solution mixture of 100 Ml of ethanoland 20 Ml of nitric acid containing 3.5 g of iodine(I), the metalnanoparticles with vacancies and dislocations in structure thereofunderwent the etching process in the prepared solution for 3 hours. As aresult, a nanocrater iron catalyst with a nanocrater form of holestructure at the center of the nanoparticles was produced.

Example 2 Preparation of Nanocrater Cobalt Catalyst

For preparation of a nanocrater iron catalyst, first of all, a cobaltfilm with thickness of about 10 nm was vapor-deposited on a siliconsubstrate at 200° C. by means of a sputtering process. Then, thedeposited substrate was plasma etched using 90 sccm of nitrogen gas witha plasma power of 700 W at 700° C. for 1 minute.

Among the above processes, the metal films separated and etched in therange of nano units by the plasma process produced a plurality ofvacancies and dislocations in inherent structure of the metalnanoparticles. Next, after preparing an iodine-containing nitricacid/ethanol solution which was a solution mixture of 100 Ml of ethanoland 20 Ml of nitric acid containing 3.5 g of iodine(I), the metalnanoparticles with vacancy and dislocation in structure thereofunderwent the etching process in the prepared solution for 3 hours. As aresult, a nanocrater cobalt catalyst with a nanocrater form of holestructure at the center of the nanoparticles was produced.

Example 3 Fabrication and Growth of Carbon Nanotubes by Using NanocraterIron Catalyst

By means of plasma chemical vapor-deposition using the nanocrater ironcatalyst prepared in Example 1, carbon nanotubes were fabricated. Moreparticularly, the carbon nanotubes were produced using the nanocrateriron catalyst together with 85 sccm of nitrogen gas and 15 sccm ofmethane gas for 8 minutes in desired conditions of plasma power of 700 Wat 900° C. under 23 Torr of pressure.

Experimental Example 1 Structural Analysis of Nanocrater Iron Catalystand Nanocrater Cobalt Catalyst

In order to analyze structure of the nanocrater iron catalyst accordingto the present invention, SEM and AFM photographs were taken forstructures of the nanocrater iron catalyst prepared in Example 1 and thenanocrater cobalt catalyst prepared in Example 2, respectively, and theresults are illustrated in FIGS. 1A to 2D.

FIGS. 1A and 1B are SEM photographs showing a nanocrater iron catalystproduced by a plasma etching and chemical etching process (PTCE).

FIG. 1A is a SEM photograph showing a nanocrater iron catalyst formed ona silicon substrate. Referring to FIG. 1A, it was found that thenanocrater catalyst was uniformly formed on the silicon substrate.Meanwhile, FIG. 1B is an AFM photograph showing enlarged condition ofone of the nanocrater iron catalysts. As a result, it was observed thata hole with a size of 14 to 18 nm was formed at the center of each ofthe nanoparticles by means of a chemical etching process.

FIGS. 2A and 2C are AFM photographs showing the nanocrater iron catalystand the nanocrater cobalt catalyst, respectively. Especially, FIG. 2A isan AFM photograph of the nanocrater iron catalyst while FIG. 2C is anAFM photograph of the nanocrater cobalt catalyst.

FIGS. 2B and 2D illustrate analysis results of surface heights measuredalong lines indicated in FIGS. 2A and 2C, respectively. Referring toFIGS. 2B and 2C, it is found that the nanocrater iron catalyst has athickness of about 14 nm while the nanocrater cobalt catalyst has athickness of about 4 nm.

Experimental Example 2 Structural Analysis of Carbon Nanotubes UsingNanocrater Iron Catalyst

In order to analyze structure of a specific nano material by using thenanocrater metal catalyst according to the present invention, SEM andAFM photographs were taken for structure of the carbon nanotubesfabricated in Example 2, and the results are illustrated in FIG. 3A to3E.

FIG. 3A is a SEM photograph showing carbon nitride nanotubes and carbonnanospheres with hollow center structure; FIG. 3B is a TEM photographshowing carbon nitride nanotubes; FIG. 3C is a TEM photograph showingcarbon nanosphere with hollow center structure; and FIG. 3D is a TEMphotograph showing two pairs of carbon nitride nanotubes.

In addition, FIG. 3E is a TEM photograph showing enlarged bottomportions of two pairs of carbon nitride nanotubes. Referring to FIG. 3E,it was found that the nanotubes had an inner diameter of 5 to 8 nm andsuch inner diameter was substantially identical to size of thenanocrater iron catalyst. Also, as shown in FIG. 3E, it can be clearlyunderstood that two pairs of carbon nitride nanotubes were all grown tohave a uniform thickness sufficient to form 3 to 8 walls.

As described above, a nanocrater metal catalyst according to the presentinvention has advantages in that: the catalyst can be used inmanufacturing a variety of nano-sized materials; and has variable sizesand structures to uniformly control number of walls of the nanomaterials, therefore, can control structures of the nano materials suchas carbon nanotubes as desired.

While the present invention has been described with reference to thepreferred embodiments and examples, it will be understood by thoseskilled in the art that various modifications and variations may be madetherein without departing from the scope of the present invention asdefined by the appended claims.

1. A nanocrater catalyst in metal nanoparticles having a nano-sizedcrater form of hole at the center of the catalyst, which has vacancy anddislocation between metal nanoparticles of the catalyst.
 2. Thenanocrater catalyst in metal nanoparticles according to claim 1, whereinmetal ingredient of the catalyst comprises at least one selected fromelements belonging to Groups 3 to 14 in the Periodic Table.
 3. Thenanocrater catalyst in metal nanoparticles according to claim 2, whereinthe metal ingredient is one or two selected from iron (Fe) and cobalt(Co).
 4. The nanocrater catalyst in metal nanoparticles according toclaim 1, wherein the hole has a size ranging from 1 to 50 nm.
 5. Thenanocrater catalyst in metal nanoparticles according to claim 1, whereinthe catalyst has a thickness ranging from 1 to 20 nm.